Dental implant

ABSTRACT

A dental implant for anchoring in bone, wherein said bone comprises an outer cortical bone section and an inner cancellous bone section is made of a body of resorbable material such as coral, having a portion capable of being wedged into the cancellous bone. The body of coral has a generally cylindrical root portion, an emergent portion capable of being wedged into said outer cortical bone section, and a transgingival coronal portion being sized to extend beyond said emergent portion to end beyond a gingival layer, and an abutment portion and a head for retention of said prosthetic device at the other end, wherein said abutment portion meets said coronal portion at an interface beyond said gingival layer. The body of coral is substantially electroplated with a suitable plating material such as gold. At least some of the root portion is absent said plating material so as to allow the bone to enter the substantially plated body of coral to resorb and replace at least some of the coral.

FIELD OF THE INVENTION

This invention relates generally to the field of dental implants, andmore specifically relates to implants that are biocompatible andresorbable by bone.

BACKGROUND OF THE INVENTION

The references listed in this specification, to the extent that theyprovide exemplary procedural or other details supplementary to those setforth herein, are specifically incorporated herein by reference.

Dental implants used to stabilize dentures or support dental crowns andbridges have been known and have been used fairly extensively in therecent past. Such prior art devices are typically comprised of threecomponents, namely, an implant component for anchoring to the bone, atransgingival component and a separate support component. The supportcomponent usually attaches to the transgingival component which, in turnattaches to the anchoring component at about the level of the bone. Anartificial tooth or bridge may then be attached to this separate supportcomponent. This support component is sometimes referred to as anabutment portion, the transgingival component is sometimes referred toas an abutment connection or the transgingival collar or thetransepithelial connection and the implant is sometimes referred to as afixture. An example of such a prior device is found in Canadian PatentNo. 1,313,597. This patent describes an implant for insertion into bonethrough an epithelial and fibrous connective tissue layer to which aprosthesis may be attached. This implant comprises a top portion forsupporting a mechanical component to which the prosthesis may beconnected and a body comprising an upper bone attachment region, whichtapers to a lower bone engagement region having a porous surface. Theupper bone attachment region comprises a substantially non-porous butbioreactive surface and this patent teaches that this results in anupper bone attachment region which is claimed to be capable of enhancingbone attachment.

However, several problems develop with an implant of this type. Inparticular, the patent teaches use of a collar 14 that is adapted to becoupled to the implant 12. However the interface between the collar 14and the implant 12 occurs at a level below the gingiva in the installedposition. Further, although the patent teaches providing recesses 40 onthe lower surface 42 of the collar 14 to compliment projections 32 ofthe implant 12 to prevent rotation between the two components, inpractice this is not effective. The attachment between the collar andthe implant is accomplished by means of a threaded screw identified as46 in FIG. 1. Such a screw has a natural tendency to become loose duringthe vigorous stresses to which an implant of this type is subjected.

To avoid problems associated with the loosening of the threaded screw46, practitioners have resorted to insertion of cement into the threadedportion to ensure a locked and non-loosening joint between the implantcomponent and the support component.

However, a basic problem with this structure and method still remains.Substantial forces are exerted upon a very small region where the screwis affixed within the jaw. These forces are focused about a small regionabout point rather than being distributed. Using a plurality of closelyset screws disadvantageously lessens the amount of material to which theimplant may be affixed.

Unfortunately, screws eventually become loose, and damage to the boneinto which they are affixed is permanent. Thus repeated re-tightening orinsertion of new screws is limited and not practicable.

It is an object of this invention to provide a "snowshoe-like" effectwherein an implant is securely affixed becoming joined to bone at amultiplicity of points over a large region.

In the aforementioned prior art implant, unfortunately, because theinterface between the collar and the implant is below the gum level, anyexcess cement will be squeezed out at the interface and may not benoticed by the practitioner since it is hidden from view. Such excessaccumulation of cement can create irritation of the gum and the bone andcan result in infection and/or implant failure. In addition, all implantsystems, (fixture, abutment connection, abutment) which have this typeof arrangement have a microgap between the fixture or implant and theabutment connection or the transgingival collar at the level of thebone. This microgap has been called an "sendotoxin generator" by someauthorities because it is a region for potential bacterial growth.

Other prior art devices include implants with threaded exteriors, whichrequire extensive and complicated methods for preparation of the gum andbone to accept the insert. As a result, such implants are difficult andexpensive to insert and specialists most often do the surgery.

This invention provides an implant and method of fabricating such whichobviates difficulties and associated problems with prior art implantsystems.

An aspect of this invention relates to the use of a resorbablebiocompatible material such as coral, to provide the overall implantstructure.

The use of these biocompatible materials is well known to assist in theregeneration of bone defects and injuries. In 1926, DeJong observed thesimilarities between the powder X-ray diffraction pattern of the in vivomineral and the hydroxyapatite (Ca₅ B(OH)(PO₄)₃, (CHA). Calciumcompounds, including calcium sulfate (Nielson, 1944), calcium hydroxide(Peltier, 1957), and tricalcium phosphate (TCP) (Albee et al., 1920),have been observed to stimulate new bone growth when implanted orinjected into bone cavities (Hulbert et al., 1983). These materials alsoexhibit good biocompatibility and compositional similarities to humanbone and tooth and can serve as resorbable or non-resorbable implantsdepending on their degree of microporosity.

Some TCP implants are known to be readily resorbable. For example,sintered TCP plugs with pore sizes between 100-200 microns have beenimplanted in rats (Bhashar et al., 1971). Very rapid bone formation wasreportedly observed at three days after implantation, and highlycellular tissue, consisting of osteoblastic and fibroblasticproliferation, was found within the pores. At one week, the size of theimplant was reduced, and new bone formation was extensive. After twoweeks, connective tissue had infiltrated throughout the ceramic. Duringthe next four weeks, the bony material within the ceramic continued tomature. Electron micrographs indicated that within clast-like cells,ceramic could be depicted in membrane-bound vesicles. The authorsconcluded that TCP implants were biodegradable, via phagocytosis, theceramic did not elicit a marked inflammatory response, and connectivetissue grew rapidly within the pores. Similar results have also beenreported by Cutright et al. (1972) who also implanted TCP in rat tibiae.In this study, the ceramic cavities were filled with osteoid and boneafter 21 days and the TCP implant was no longer detectable after 48days.

Larger implants in dogs are reported to elicit slower responses. Cameronet al. (1977) found that TCP implants in dog femurs were completelyinfiltrated with new bone by four weeks. However, after six weeks, therate of new bone growth had slowed as the TCP was resorbed.Additionally, only 15% of a 2 cm×2 cm iliac TCP implant in dogs wasresorbed after 18 months (Ferraro et al., 1979). Koster et al. (1976)reported the testing of the calcium phosphate formulations monocalciumphosphate, dicalcium phosphate, tricalcium phosphate, tetracalciumphosphate, and combinations consisting of 20% monocalcium phosphate and80% of either di-, tri- or tetracalcium phosphate as implant materialsin dog tibiae. These investigators tested both dense ceramics and porousceramics with pore sizes between 800-1000 microns. They reported thattissue compatibility is dependent on the CaO/P₂ O₅ ratio. All materialswith ratios between 2/1 and 4/1 are compatible with the optimum ratiobeing about 3/1 for TOP. After 10 months, Koster et al. (1977) foundthat tetracalcium phosphate was resorbed only to a minor extent, butthat TCP demonstrated lamellar bone growth throughout its pores. Bothwere found to be tissue compatible. The authors stated that the 3/1material was not as strong as the 4/1 material and suggested that TCPshould be used only in low stress areas while tetracalcium phosphatecould be used in high stress environments. Jarcho et al. (1976, 1977)reported the development of a process for preparing dense,polycrystalline, calcium hydroxyapatite (CHA), with the empiricalformula 2(Ca₅ (PO₄)₃ OH) or (3Ca₃ (PO₄)₂)Ca(OH)₂. In this study, plugswere fabricated at 100% density and implanted in dogs. No evidence oftissue inflammation occurred, and in contrast to the porous TCP implantsdescribed above, little resorption or biodegradation was observed aftersix months. Holmes (1979) reported that resorption did occur in porousCHA structures. These results led deGroot (1980) to suggest that allcalcium phosphates are degradable (resorbable), but the rate isdetermined by the degree of microporosity. A dense calcium phosphatewith negligible porosity would thus degrade only nominally. Theseresults seem to be verified by Farris et al. (U.S. Pat. No. 4,673,355),who claim biocompatible materials with good properties over the range ofCa/P atomic, or molar, ratios from 0.1 to 1.34. These ratios convert toCaO/P₂ O₅ ratios between 0.2 and 2.68, lower than the 3.0 ratiosuggested above. They suggest that the Ca/P or CaO/P₂ O₅ ratio is notcritical for implant applications. Ca/P ratios in the range 0.1 to 2.0probably show satisfactory biocompatibility. Capano (1987) found that aCa/P ratio of 0.5, which corresponds to calcium metaphosphate ("tCMP"y),has the best biocompatibility when implanted in small animals. As theapatites are nearly identical in properties and chemical compositions tobone and tooth enamel, a considerable amount of synthetic effort hasbeen done in this area. Patents in this area include: U.S. Pat. Nos.4,046,858; 4,274,879; 4,330,514; 4,324,772; 4,048,300; 4,097,935;4,207,306; and U.S. Pat. No. 3,379,541. All of these patents areincorporated herein by references. Several patents describe methods fortreating apatite materials to render implantable shapes. These methodsof heating and compaction under pressure in molds produce solid porousarticles in various shapes. These patents include: U.S. Pat. Nos.4,673,355; 4,308,064; 4,113,500; 4,222,128; 4,135,935; 4,149,893; andU.S. Pat. No. 3,913,229. Several patents speak to the use of laserradiation to bond apatite materials to tooth and other surfaces, forexample, U.S. Pat. No. 4,673,355 and U.S. Pat. No. 4,224,072. Otherpatents describe the use of particulate or compacted apatite inconjunction with various compounds, filler, and cements, for example,U.S. Pat. Nos. 4,673,355; 4,230,455; 4,223,412; and U.S. Pat. No.4,131,597. The aforementioned patents are all incorporated herein byreference. The above discussion indicates that calcium phosphates orcompounds, such as CHA that are substantially TCP (Monsanto, forexample, markets CHA as TCP), are useful for a variety of bioceramicapplications because they are biocompatible and can be fabricated intoshapes that have a desirable combination of strength, porosity, andlongevity for particular sorbable and non-sorbable needs. Virtually anycalcium and phosphate source can be used to prepare materials ofinterest.

This is explained in more detail in U.S. Pat. No. 5,639,402 issued Jun.17, 1997 and entitled Method for fabricating artificial bone implantgreen parts, incorporated herein by reference.

Some more recent advances are the development of hydroxyapatite (CHA)and calcium phosphate powders that can be processed to yield porousresorbable bone facsimiles (U.S. Pat. No. 4,673,355); the development ofthe SLS™ process for directly shaping complex porous structures fromthermally fusible polymer/ceramic powders without molds (U.S. Pat. No.5,076,869); the development of low temperature infiltration andcementing techniques to prepare and replace the polymer binder withceramic binder (U.S. Pat. No. 5,284,695); and the development oftechniques for converting computed tomographic ("hCT"y) information intothree-dimensional mathematical files that can automatically guide theSLS™ process (Levy et al., 1992; Levy et al., 1994).

More recent work has been directed at expanding the utility of the SLS™apparatus by preparing polymer-coated ceramic powders from spray driedmixtures of water, inorganic particulate, and a custom-synthesized,emulsified, nanometer-sized, polymer binder (Barlow, 1992; Vail et al.,1992). Ceramic composites made by this approach are relatively large,10-50 microns, agglomerates of polymer-coated inorganic particles. Theseagglomerate powders may spread easily into uniform layers and fusereadily in the SLS™ machine to yield porous "green" parts that haverelative densities near 50%, excellent connected internal porosity, andsufficient strengths to be easily handled and shipped. Interconnectedpores in bioceramics are often difficult to achieve and are veryimportant in fostering bone growth and for preparing metalmatrix/ceramic parts, artificial hips. Polymethyl methacrylate (PMMA)has also been used to form green composites with alumina and withsilica/zircon (U.S. Pat. No. 5,284,695). In this process, an appropriateceramic silicate colloid is used to infiltrate the connected pores ofthe polymer-bound green part, the colloid is solidified below the fusiontemperature of the binder to maintain part geometry, the binder is thenthermally removed and the part fired at typically 1000 degree C. to formporous, all ceramic parts that are suitable for use as cores and moldsfor metal castings. Such parts typically have only a 1% linearshrinkage, relative to the green state. Their strengths and porositiescan be adjusted by additional infiltration and firing treatments. Lagowand co-workers have recently described the chemical synthesis of highstrength CHA (U.S. Pat. No. 4,673,355) and long-chain calciumpolyphosphate bioceramic powders ("5CPB"e) (Capano, 1987; Nelson et al.,1993). CPB powder is a pure calcium phosphate material with condensedphosphate chains (as shown below) with degrees of polymerization oftengreater than 120. These materials produce sintered materials that havecompressive strengths greater than 200,000 psi and flexural strengths inexcess of 20,000 psi. These strengths are about twice that of porcelainused to make dental crowns. Using the Lagow CHA material, Lagow andFriedman have recently completed the first successful, year duration,mandible implant in canine. Work with CPB implants has demonstrated byelectron microscopy backscattering that new bone growth occupied nearly55% of the volume of a CPB implant in the alveolar (tooth bearing) ridgeof a dog, after only four months (Nelson et al., 1993).

It is an object of this invention to provide a dental implant thatovercomes many of the disadvantages of known implants.

It is an object of this invention to provide an implant that will besubstantially resorbed and replaced with bone.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a dental implant foranchoring in bone, wherein said bone comprises an outer cortical bonesection and an inner cancellous bone section, said implant comprising:

a body of coral, having a portion capable of being wedged into thecancellous bone, the body of coral having a generally cylindrical rootportion, an emergent portion capable of being wedged into said outercortical bone section, and a transgingival coronal portion being sizedto extend beyond said emergent portion to end beyond a gingival layer,and an abutment portion and a head for retention of said prostheticdevice at the other end, wherein said abutment portion meets saidcoronal portion at an interface beyond said gingival layer, the body ofcoral being substantially electroplated with a suitable platingmaterial; some of the root portion being absent said plating material soas to allow the bone to enter the substantially plated body of coral toresorb and replace at least some of the coral.

In accordance with the invention, there is provided a dental implant foranchoring in bone, wherein said bone comprises an outer cortical bonesection and an inner cancellous bone section, said implant comprising:

a body of coral, having a portion capable of being wedged into thecancellous bone, the body of coral having a root portion, an emergentportion capable of being wedged into said outer cortical bone section,and a transgingival coronal portion being sized to extend beyond saidemergent portion to end beyond a gingival layer, and a crown portion,wherein said crown portion meets said coronal portion at an interfacebeyond said gingival layer, the body of coral being substantiallyelectroplated with a suitable plating material as to substantiallyencapsulate the coral above the emergent portion; some of the rootportion being absent said plating material so as to allow the bone toenter the substantially plated body of coral to resorb and replace atleast most of the coral.

In accordance with the invention, there is provided a dental implant foranchoring in bone, comprising:

a body of resorbable material, having a root portion capable of beingcoupled with the bone and an upper portion adjacent the root portion theupper portion of the resorbable material being substantially coated witha suitable metallic material as to substantially encapsulate theresorbable material above the root portion; at least some of the rootportion being absent said plating material so as to allow the bone toenter the substantially plated body of the resorbable material to resorband replace at least most of the resorbable material.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described inaccordance with the drawings in which:

FIG. 1 is a diagrammatic view of an exposed bone region after surgicallyexposing a region between two spaced teeth;

FIGS. 2a to 2d illustrate the implant at various stages in production;

FIG. 3 is a cross-sectional partial view of the electroplated resorbableimplant;

FIG. 4 is a cross sectional view of an alternative embodiment wherein apost is affixed to the resorbable implant prior to electroplating.

DETAILED DESCRIPTION

Turning now to FIG. 1 two teeth 10 and 12 are shown having a spacedregion therebetween wherein a tooth had previously been extracted.Surgically flaps 14a and 14b of tissue are shown which expose the tissue18 and bone 16 below in a conventional manner prior to wedging animplant into the inner cancellous bone region 16.

The implant in accordance with this invention is preferably made of abio-resorbable material such as coral that has been substantially coatedwith a metallic material such as gold. However, it is essential toprovide a region or a plurality of sub-regions of the coral absent ofplating material, to allow bone, adjacent thereto to make contact withand digest the coral.

Conveniently, the coral can be coated with the metallic material by wayof electroplating. When the coral becomes coated with the platingmaterial, the metallic material penetrates the pores within the coraland becomes well anchored.

Electroplating is well known and relates to the coating of an objectwith a thin layer of some metal through electrolytic deposition. Theprocess is widely used, for the purpose of rendering a lustrousnon-corrosive finish on some article. In electroplating the generalobject is to employ the article to be plated as the cathode in anelectrolytic bath composed of a solution of salt of the metal beingplated. The other terminal, the anode may be made of the same metal, orit may be some chemically unaffected conductor. A low-voltage current ispassed through the solution, which electrolyzes and plates the cathodicarticles with the metal to the desired thickness.

A variety of methods are described for electroplating of non-conductivematerials; for example, U.S. Pat. No. 5,632,927 in the name of Ferrier,et. al. issued May 27, 1997, entitled Process For Preparing ANon-Conductive Substrate For Electroplating discloses the modificationof carbon particles for achieving enhanced plating upon a non-conductivesurface which has been previously treated with the modified carbonparticles.

U.S. Pat. No. 5,597,471 in the name of Ragge, et. al. issued Jan. 28,1997 entitled Solution For Coating Non-Conductors With ConductivePolymers and their Metallization Process discloses a process formetallizing non-conductive surfaces, by treating the non-conductivesurface with a solution containing at least one suspended or soluteoxidation agent, contacting the treated non-conductive surface with anacidic solution containing at least one water soluble polymer selectedfrom the group consisting of homopolymers and copolymers, and at leastone aromatic compound which chemically polymerizes the water-solublepolymer and the aromatic compound to form a conductive polymer, andelectroplating the conductive polymer. Each water-soluble polymercontains uncharged structural elements or is cationic polyelectrolyte.Additionally, each water soluble polymer is capable ofprotonizing/deprotonizing reactions, formation of hydrogen bridgecompounds and van der Waals interactions.

Other United States Patents that relate to electroplating non-conductivematerials are: U.S. Pat. No. 4,374,709, 5,492,613, and 5,589,270 allincorporated herein by reference.

FIGS. 2a to 2d illustrate the implant at various stages of maufacture inaccordance with a first embodiment. A bio-resorbable material in theform of a coral block 20 is first provided as the base material for theimplant. The coral block 20 is sized and shaped in such a manner as tobe suitable for fitting within the opening defined by the exposed bone16 between teeth 10 and 12. In a preferred embodiment shown in FIG. 2b,the coral 20 is shaped in such a manner as to have at an upper end, anabutment 22 for cementing to a complementary under surface of a crown(not shown). This embodiment obviates the requirement for screws orsimilar attachments.

FIG. 2c illustrates the coral implant 20 after having been coated via aplating process wherein a substantial portion of the implant is platedwith gold or other suitable metallic material 24. As is shown, thebottom portion of the implant is un-plated as it is coated with aplating resistive material such as wax, prior to electroplating. Thepurpose of not plating a portion of the coral, or removing a portion ofthe plating on the coral is that the coral material must be in directcontact with the bone 16 for digestion/resorbing of the coral by thebone 16 to take place.

Alternatively, the entire coral implant may be coated by electroplating,and later, the bottom portion ground to remove the coral coatingdeposited thereon.

FIG. 2d shows the implant after having undergone a preferred but notrequired step. After the implant is electroplated, the gold coating isthen used as a substrate for depositing thereon a layer of titanium 26,through a process such as vapour deposition. This titanium layerenhances the interface attachment between the gum tissue adjacent thebone 16, and the implant.

The benefits of using titanium are well known and described in U.S. Pat.No. 5,573,401 in the name of Davidson, et. al., issued Nov. 12, 1996entitled Biocompatible, low modulus dental devices discloses dentaldevices (including implants, abutments, bridges, screws, and orthodonticappliances) that are fabricated from low modulus, biocompatible,non-toxic Ti--Nb--Zr alloys. The dental implants provide abiomaterial-to-bone interface that results in significant attachmentbetween implant and bone. The implants may be supplied with a porouscoating or macro-texture to promote bone attachment and stabilization ofthe implant in the jawbone.

Referring now to FIG. 3, a partial cross-section of an implant inaccordance with the invention is shown (not to scale); the adjacentgold-coated and coral regions in the illustration are shown magnified toillustrate the nature of the bond therebetween. Since the coral is asemi-porous substance, the gold plating enters the pores within thecoral and essentially forms hook-like attachments within the coralsubstrate.

After the implant is surgically placed into the bone 16, the coral isdigested/resorbed by the bone 16. Once the resorption is essentiallycomplete, and the coral is replaced by bone the implant is immovable.Obviously, the aforementioned problems and difficulties associated withprior art implants attached by screws are obviated by this invention.

Numerous other embodiments may be envisaged without departing from thespirit and scope of the invention.

For example, instead of shaping the upper portion of the coral to havean abutment for attaching to a crown, a metal screw or post 40 can beaffixed into the coral, prior to electroplating. After electroplatingthe coral and protruding screw head or post, the plated screw head orpost being integral with the coral provides a surface for affixing tothe undersurface of the crown. This is shown in FIG. 4. Once thescrew/post is electroplated and integrated as a monolithic structure,the "snowshoe-like" effect is achieved once the device is implanted.

In another embodiment, instead of implanting for dental purposes, aplated biocompatible implant as described according to the invention isimplanted in bone matter other than the jaw for attaching to aprosthetic device or the like. The use of the plating distributes forceexerted upon a prosthetic device more evenly across new bone materialand therefore is advantageous.

What is claimed is:
 1. A dental implant for anchoring in bone, whereinsaid bone comprises an outer cortical bone section and an innercancellous bone section, said implant comprising:a body of coral, havinga portion capable of being wedged into the cancellous bone section, thebody of coral having a generally cylindrical root portion, an emergentportion capable of being wedged into said outer cortical bone section,and a transgingival coronal portion being sized to extend beyond saidemergent portion to end beyond a gingival layer, and an abutment portionand a head for retention of said prosthetic device at another other end,wherein said abutment portion meets said coronal portion at an interfacebeyond said gingival layer, the body of coral being substantiallyelectroplated with a suitable plating material; at least some of theroot portion being absent said plating material so as to allow the boneto enter the substantially plated body of coral to resorb and replace atleast some of the coral.
 2. A dental implant for anchoring in bone,comprising: a body of resorbable material, having a root portion capableof being coupled with the bone and an upper portion adjacent the rootportion the upper portion of the resorbable material being substantiallycoated with a suitable metallic material so as to substantiallyencapsulate the resorbable material above the root portion; at leastsome of the root portion being absent said metallic material so as toallow the bone to enter the body of the resorbable material to resorband replace at least most of the resorbable material.
 3. A dentalimplant as defined in claim 2, wherein the resorbable material iscomprised of coral.
 4. A dental implant as defined in claim 3, whereinthe coral is coated with the suitable metallic material byelectroplating the material onto the coral.
 5. A dental implant asdefined in claim 4, wherein the suitable metallic material comprisesgold.
 6. A dental implant as defined in claim 4, wherein at least someof the gold is further coated with titanium.
 7. A dental implant asdefined in claim 6, wherein the titanium is coated over the gold by avapour deposition process.
 8. A dental implant as defined in claim 7,wherein the titanium is coated over the gold in such a manner as to formattachments of titanium for attaching to bone, adjacent thereto whenimplanted.
 9. A dental implant as defined in claim 3, wherein at leastsome of the further electroplated material is further coated bytitanium.
 10. A dental implant as defined in claim 2, wherein the uppersurface of the upper portion of the resorbable material includes anabutment for attaching a crown thereto.
 11. A dental implant as definedin claim 10, wherein the resorbable material is coral, and wherein thecoral is shaped in such a manner as to form the abutment.
 12. A dentalimplant as defined in claim 11, wherein the abutment is coated with themetallic material.
 13. A dental implant as defined in claim 12, whereinthe coated material coated on the abutment is applied by electroplating,and wherein the metallic material comprises gold.
 14. A dental implantas defined in claim 2 including a post within and protruding the uppersurface of the resorbable material for mating with a crown.
 15. A methodof making a dental implant comprising the steps of:providing aresorbable substrate suitably sized and formed to be implanted intocancellous bone of a patient; coating at least a portion of theresorbable substrate with a metallic material; ensuring that at least aportion of the resorbable substrate is absent the metallic material;providing an upper surface that is compatible with a lower surface of acrown for mating therewith.
 16. A method as defined in claim 15 whereinthe metallic material is gold.
 17. A method as defined in claim 16further comprising the step of coating the at least some of the goldwith titanium.
 18. A method as defined in claim 16 wherein the coatingstep is performed by electroplating.
 19. A method as defined in claim17, wherein the titanium coating is applied by vapour deposition.